Efficient sampling design for larvae of American lobster

Abstract

For 13 years, lobster larvae were collected from the same 23 stations at approximately weekly intervals for the duration of the larval season (Scarratt, 1964). Using the most complete 8 years of collections, we produced several data subsets for each year by reducing the number of sampling dates and the number of stations per date. Our analyses were confined to the fourth and final larval stage, the most likely stage to be correlated with fishery yields. The means and confidence intervals for annual larval abundance were calculated on the data subsets and compared with the full dataset. We conclude that the usual lobster larval sampling frequency of weekly, or more often, was unnecessary. Tows taken at 10 or 14 stations per week for 4 weeks of the 9 week larval season represented well the mean and confidence intervals on the full dataset. These choices remained the best after the costs of sampling were included. Further cost reduction could be achieved without loss of precision by removing collections from the net after every second, rather than after every tow. Mean annual density was found to be a good index of annual larval production. Thus, the collections during 4 weeks represented annual abundance and annual production.